Planetary detent for rotary devices

ABSTRACT

A fluted disc is maintained concentrically within an internally serrated ring by a plurality of elastic cylinders disposed therebetween and positioned to provide a zero summation of forces through the central axis of the mechanism. The ring is fixed to the rotary device housing and a manually operable control shaft for the latter extends axially through the disc which is keyed for rotation with the shaft. Rotation of the disc rolls the elastic cylinders along the surfaces of the disc and ring to seat in the next adjacent flutes and serrations, respectively, the cylinders being compressed when passing over the ridges between adjacent flutes and serrations and rapidly restoring upon passing beyond the ridges to positively seat within the next flutes and serrations. The detent torque may be readily varied by increasing or decreasing the number of elastic cylinders. While mathematical and geometrical relationships are established to permit a detent mechanism to be provided for almost any rotary application, a primary relationship to be established in each instance requires that the chord length of the flutes be identically equal to the chord length of the serrations to permit continuous rotary operation.

United States Patent Williams, III

[451 Sept. 26, 1972 [54] PLANETARY DETENT FOR ROTARY DEVICES [72]Inventor: Robert C. Williams, III, Smithfield,

[73] Assignee: Cutler-Hammer, Inc., Milwaukee,

Wis.

[22] Filed: Jan. 6, 1971 [21] Appl. No.: 104,294

[52] US. Cl ..74/527, 200/166 SD [51] Int. Cl. ..G05g 5/06 [58] Field ofSearch ..74/527, 531, 10.41; 200/ 166 SD [56] References Cited UNITEDSTATES PATENTS 3,570,325 3/1971 Kroll et al ..74/527 3,185,787 5/1965Deibel et a1 ..74/527 X 3,293,382 12/1966 Lewandowski et al. .74/527 XPrimary Examiner-W. F. ODea Assistant Examiner-F. D. ShoemakerAttorney-Hugh R. Rather and William A. Autio [5 7] ABSTRACT A fluteddisc is maintained concentrically within an internally serrated ring bya plurality of elastic cylinders disposed therebetween and positioned toprovide a zero summation of forces through the central axis of themechanism. The ring is fixed to the rotary device housing and a manuallyoperable control shaft for the latter extends axially through the discwhich is keyed for rotation with the shaft. Rotation of the disc rollsthe elastic cylinders along the surfaces of the disc and ring to seat inthe next adjacent flutes and serrations, respectively, the cylindersbeing compressed when passing over the ridges between adjacent flutesand serrations and rapidly restoring upon passing beyond the ridges topositively seat within the next flutes and serrations. The detent torquemay be readily varied by increasing or decreasing the number of elasticcylinders. While mathematical and geometrical relationships areestablished to permit a detent mechanism to be provided for almost anyrotary application, a primary relationship to be established in eachinstance requires that the chord length of the flutes be identicallyequal to the chord length of the serrations to permit continuous rotaryoperation.

6 Claims, 9 Drawing Figures PLANETARY DETENT FOR ROTARY DEVICESBACKGROUND OF THE INVENTION This invention relates to detent mechanismsparticularly well suited for use with rotary devices such as rotaryelectrical switches or the like.

Detent mechanisms for rotary switches serve as indexing means forestablishing positive contact engagement. Such mechanisms typicallyemploy complemen tally formed recesses and projections which are biasedinto engagement by spring means. An operation of the switch causes thecomplemented formations to be cammed apart against the bias of thespring means and to re-engage with another complementally formedportion. The camming motion is usually in a direction normal to thetravel of the movable member of the switch and introduces considerablesliding friction forces, wear and dust particle problems for the switch.The size of the switch establishes limits in size and strength of thespring means as well as in the size of the comple- SUMMARY OF THEINVENTION It is a primary object of this invention to provide a detentmechanism for use in a continuously rotating operational mode whichoperates totally without sliding friction in any force-loaded directionof the mechanism components.

It is a further object of this invention to provide a detent mechanismof the foregoing type which may be readily adapted to rotary devices ofwidely varying sizes.

It is a further object of this invention to provide a detent mechanismof the foregoing type wherein the operational torque may be simply andreadily varied.

It is still another object of this invention to provide a detentmechanism of the foregoing type which may be readily and inexpensivelymanufactured.

These and other objects and advantages of this invention will becomemore readily apparent in the following specification and claims whenread in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of arotary electrical switch incorporating the detent mechanism of thisinvention;

FIG. 2 is an enlarged cross-sectional view taken along the line 22 inFIG. I and showing the detent mechanism of this invention in elevation;l

FIGS. 3a, 3b and 3c are elevational views of the detent mechanism ofthis invention showing modifications thereof;

FIGS. 4a, 4b and 4c are fragmentary views of portions of the detentmechanism sequentially depicting an operation of the mechanism; and

FIG. 5 is a fragmentary view of a portion of the detent mechanism ofthis invention with certain dimensional references applied thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A one hole mounting rotaryelectrical switch 2 is shown in FIG. 1 of the drawings. The switch 2includes a metallic frame 4 having a threaded mounting bushing 6 securedthereon. The detent assembly 8 of this invention and a rotary electricalswitch deck 10 are secured in tandem to the rear of frame 4 by threescrews 12 which project rearwardly through alined openings in the frame4, detent assembly 8 and switch deck 10 to receive nuts 14 thereon. Thedetent assembly 8 includes a cover plate 16 disposed between frame 4 andan outer track member 18 of the detent assembly and an insulating plate20 disposed between the outer track member 18 and the switch deck 10.

Switch 2 further includes a centrally disposed axially extendingoperating shaft 22 which appears in crosssection in FIGS. 2 through 4c.While not specifically shown in the drawings, shaft 22 is joumalled forrotation within frame 4 and bushing 6 to extend in opposite directionsthereof, a first end extending beyond the outer end of bushing 6 to havea knob 24 secured thereto and the opposite end extending through detentassembly 8 into switch deck 10. The last mentioned end of shaft 22 isformed to have a square cross-sectional configuration to becooperatively received within complementary shaped openings in a movablemember of the detent assembly and in the rotary contact structure ofswitch deck 10 to operate the switch.

With particular reference to FIG. 2, the aforementioned outer track 18may be seen to be a ring having a continuously serrated inner diameter26. Outer track member is preferably formed of an electrical insulatingmaterial and is provided with three clearance holes 28 for screws 12. Ifdesired the holes 28 may be formed substantially oversized for screws 12and bushings 30 provided therein to aid in centering the detent on therotary device in assembly if tolerances are not held closely.

Detent assembly 8 further includes a centrally located disc 32 alsopreferably formed of an electrical insulating material and having acontinuously fluted periphery 34. Disc 32 is keyed for rotationalmovement with shaft 22 by means of a central square-shaped aperture 36through which the square portion of shaft 22 extends. The thickness ofdisc 32 is somewhat less than that of outer track member 18 to permitfree rotational movement of disc 32 between cover plate 16 andinsulating plate 20.

A plurality of elastic cylinders 38 are positioned between the flutedperiphery 34 of disc 32 and the serrated inner diameter 26 of ringshaped outer track 18 to rest within oppositely disposed ones of theflutes and serrations. As will be brought out later, certain of theoppositely disposed flutes and serrations cooperate to form opposed arcson a common circle whose diameter is substantially identical to thediameter of each of said elastic cylinders 38. The exact number ofelastic cylinders 38 used in a detent assembly varies according to theamount of torque desired for the operating shaft; where greater torqueis required a greater number of elastic cylinders 38 are employed.Regardless of the number of cylinders employed, however, the same arealways physically positioned within the detent assembly in a mannerwhereby the summation of the forces presented by the cylinders throughthe central axis of shaft 22 is equal to zero. The exemplary detent inFIG. 2 employs three cylinders 38 spaced at 120 degree intervals. FIGS.3a through 3c depict the same detent assembly employing two, four andsix cylinders 38, respectively, the cylinders in each instance beingequally arcuately spaced to provide a zero summation of forces throughthe central axis.

The particular detent assembly 8 shown in the drawings is designed toestablish 45 indexing positions for shaft 22 and switch deck 10. Withreference to FIGS. 40-40 and particularly to FIG. 4a, a portion of thedetent assembly is redrawn in enlarged scale to show the upper cylinder38 of FIG. 2 and fragmentary portions of the serrated inner diameter 26,disc 32 and shaft 22. It is to be understood that the operationalmovement described in connection with the upper elastic cylinder 38 issimultaneously identical for each cylinder 38 employed.

An initial position of the shaft 22 and detent assembly 8 is shown inFIG. 4a wherein elastic cylinder 38 rests in a serration on innerdiameter 26 defined by ridges S1 and S2 and in a flute on the periphery34 of disc 32 defined by ridges F1 and F2. Rotation of the shaft 22 is acounter-clockwise direction as viewed in the drawings and indicated byarrow 40 drives disc 32 therewith by virtue of the aforedescribedcomplemental square shapes of shaft 22 and aperture 36 in disc 32.Counter-clockwise movement of disc 32 rolls the elastic cylinder 38along the periphery 34 and along the inner diameter 26 to cause thepoints F2 and S2 to imbed into and compress the cylinder 38 as shown inFIG. 4b. Maximum compression of the cylinder 38 is reached when thepoint F2 is rotated to fall on a common immaginary straight line throughthe point S2, the center of cylinder 38 and the axial center of theshaft 22. Continued rotation of disc 32 rotates the point F2 beyond theabove described immaginary line and the elastic cylinder 38 begins torestore itself back to its original shape. The restoring force ofcylinder 38 is exerted radially outwardly thereof against its points ofcontact S2 and F2 to provide a driving force in the counter-clockwisedirection for disc 32.

Disc 32 continues to rotate until the point F3 of the next adjacentflute engages the periphery of the elastic cylinder 38 to establish asubsequent rest position for the detent as shown in FIG. 4c. Inaccordance with a novel feature of this invention, the point S3 of thenext adjacent serration engages the periphery of elastic cylinder 38simultaneously with the aforementioned engagement of point F3 therewithand the new rest position is positively established. With reference toFIG. 4c, it can be seen that in this position, the cylinder 38 now liesbetween the arcs bounded by points S2 and S3 on the inner diameter 26and by points F2 and F3 on the periphery 34 of disc 32. The shaft 22 isnow displaced 45 counter-clockwise from the initial position.

The simultaneous engagement of the points S3 and F3 with the elasticcylinder 38 permit the detent assembly 8 to be used in a continuouslyrotating mode without the disc and outer track getting out ofsynchronism. If the point S3 was not to engage the cylinder 38 when thelatter seats firmly between the points F2 and F3, a small increment oftravel of cylinder 38 along the serrated inner diameter 26 would remainto be initially traversed during the next successive indexing movementof disc 32. It should be apparent that the remaining increment of travelis cumulative over the individual positions and that if similarconditions exist for each of the positions, successive indexing in agiven rotational direction will cause the cylinder 38 to eventuallystraddle a ridge between adjacent serrations when it is firmly seated ina flute on disc 32, thereby causing the disc 32 to be outofsynchronization with the outer track 18 and the switch deck 10. Asimilar situation exists when a small increment of overtravel is presentbetween the cylinder 38 and a serration on the inner diameter 26.

A primary consideration in the design of the detent of this invention torender it particularly well suited for continuously rotating operationis the establishment of equal chord length between the chords 42 of theflutes on disc 32 and the chords 44 of the serrations on inner diameter26. The chords 42 and 44 are shown in FIG. 5 as the opposite ends of arectangle inscribed within the cylinder 38, thereby geometricallyestablishing their equal length. With the distances between the ridgesof the flutes and serrations being equal, the elastic cylinder 38 willnecessarily seat positively within the cooperating flute and serrationand no overtravel or undertravel of the cylinder will be present.

In conjunction with the establishment of equal chord lengths, certainmathematical relationships are also provided which aid in constructing adetent mechanism for any given rotary device. Referring particularly toFIG. 5, a pair of lines are shown radiating from the rotational centerof the detent mechanism to the opposite ridges of a flute on periphery34 of disc 32 to define an included angle A therebetween. Similarly, asecond pair of lines radiate from the center to the opposite ridges of aserration on inner diameter 26 to define an included angle Btherebetween. From the sequential views of FIGS. 4a-4c and thedescription associated therewith, it can be seen that the total angulartravel of shaft 22 and disc 32 per single indexing movement is equal tothe sum of angles A and B. To be workable with a rotary device, thequotient of 360 divided by the sum of angles A and B must be a wholenumber. Additionally, it is apparent from FIG. 5 that angle A is greaterthan B and while the exact ratio of A to B may vary if necessary, it hasbeen found most convenient to require A to be twice as great as B.Therefore, given a number of positions for a rotary device, the indexingangle and the angles A and B may be calculated.

Again referring to FIG. 5, it can be seen that the radial distances fromthe rotational center of the detent mechanism to the ridges of theflutes on disc 32 and,

serrations on inner diameter 26 are dimensioned as X and Y,respectively. Knowing the values for angles A and B and that chords 42and 44 are equal, a relationship between X and Y can be geometricallyshown to exist as Y= sin B/2/sin A/2. By choosing a value for X whichphysically adapts the mechanism to the size of the particular rotarydevice, a proportionate value of Y may be determined from the foregoingformula.

In the drawings, it can be seen that the flutes and serrations arepreferably formed arcuately of a radius equal to the radius of theelastic cylinders 38, although they could be formed of a lesser radiusor by V-shaped shown in FIG. 5 and is provided by another geometricalrelationship stated by theformula D Iii/X Y 2XY cos (A /2 The factor nis determined from a durometer reading giving the hardness of thematerial to be used for the cylinders 38 and increases the diameter D ininverse proportion to the hardness of the material. Thus, in addition toproviding more elastic cylinders 38 as mentioned earlier, the torque mayalso be increased by providing larger and/or less resilient cylinders 38j Thus there is provided herein a basic detent mechanism which may beused in a continuously rotating mode without getting out of synchronism,which operates solely with rolling friction and which may be readily andeasily modified to increase or decrease the detent torque desired. Inaddition, the detent mechanism provided herein is a thin self-containedunit which may be readily added to a rotary device or may be easilyincorporated as an integral portion of a rotary device. The mathematicalrelationships provided herein permit the basic operational design of themechanism to be readily adopted to a wide range of rotary devicesregardless of the number of positions required or physical size of thedevices Iclaim:

l. A detent mechanism for use with a rotary device comprising, incombination: v

a first member having a generally cylindrical internal surface and aplurality of inwardly projecting, axially extending ridges formed onsaid internal surface at equally spaced intervals therealong;

a second member having a generally cylindrical external surface and aplurality of outwardly projecting, axially extending ridges formed onsaid external surface at equally spaced intervals therealong disposedconcentrically within said first member, the chord length betweenadjacent ridges on said second member being identically equal to thechord length between adjacent ridges on said first member;

a plurality of circular elastic members disposed between said first andsecond members each engaging at the periphery thereof with adjacentpairs of ridges on said first and second members;

means connecting one of said first and second members to a stationaryportion of said rotary device and means connecting the other of saidfirst and second members to a movable portion of said rotary device andto an operator means to effect rotational movement of said other memberrelative to said one .member when operated, said movement causing saidelastic members to roll along said internal and external surfaces ofsaid first and second members, respectively, to be compressed betweencooperating ridges on said first and second members as the respectiveridges 5 become radially aligned and to sequentially expand as saidridges move beyond radial alignment, said elastic members engaging withsucceeding adjacent pairs of ridges on said first and second members toestablish a rotationally displaced position of one of said first andsecond members with respect to the other thereof. 2. The combinationaccording to claim 1 wherern said elastic members are cylindersextending axially in directions parallel to said ridges.

3. The combination according to claim 2 wherein said ridges are formedby adjacent concave grooves formed in said internal surface of saidfirst member and in said external surface of said second member, saidgrooves having a radius substantially equal to that of said elasticcylinders.

4. The combination according to claim 3 wherein said first member isconnected to the stationary portion of said rotary device and saidoperator means for said rotary device is rotationally v keyed to saidsecond member to cause rotational movement thereof relative to saidfirst member.

5. The combination according to claim 1 wherein:

A represents the included angle between a pair of imaginary linesradiating from the axial center of said second member to respective onesof an adjacent pair of ridges on the external surface of said secondmember;

B represents the included angle between a pair of imaginary linesradiating from the axial center of said first member to respective onesof an adjacent pair of ridges on the internal surface of said firstmember; 4

X represents the radial distance from the axial center of said firstmember to the ridges on the internal surface thereof;

Y represents the radial distance from the axial center of said secondmember to the ridges on the external surface thereof;

the sum of angles A and B is the indexing angle for the detent and isdivisible into three hundred sixty to result in a whole number quotient;and

said first and second members are constructed according to therelationship Ysin A/2 X 8/2.

6. The combination according to claim 5 wherein D 50 represents thediameter of said circular elastic members and is found .by the formulawhere n is a factor determined from the hardness of 55 the material ofsaid elastic cylinder and increases the diameter D inversely toincreasing hardness of the material.

ggz gg I UNITED STATES PATENT OFFICE (JETIFICATE or Patent No. 3 93 475Dated Se gtember 26, 1972 Inventor) Robert C. Williams; III

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

C"0lufnn 3, line 26, reads "shaft 22 is a" and should be --shaft 22 ina-- Column 6, line 48, reads Y sin A/2 X B/Z" and should be --Y IsinA/ZX sin B/2-'- Signed and sealed this 3rd day of April 1973.

(SEAL) Attest-z EDWARD NLFLETCHERJRQ I 7 ROBERT GOTTSCHALK Commissionerof Patents Attesting Officer

1. A detent mechanism for use with a rotary device comprising, incombination: a first member having a generally cylindrical internalsurface and a plurality of inwardly projecting, axially extending ridgesformed on said internal surface at equally spaced intervals therealong;a second member having a generally cylindrical external surface and aplurality of outwardly projecting, axially extending ridges formed onsaid external surface at equally spaced intervals therealong disposedconcentrically within said first member, the chord length betweenadjacent ridges on said second member being identically equal to thechord length between adjacent ridges on said first member; a pluralityof circular elastic members disposed between said first and secondmembers each engaging at the periphery thereof with adjacent pairs ofridges on said first and second members; means connecting one of saidfirst and second members to a stationary portion of said rotary deviceand means connecting the other of said first and second members to amovable portion of said rotary device and to an operator means to effectrotational movement of said other member relative to said one memberwhen operated, said movement causing said elastic members to roll alongsaid internal and external surfaces of said first and second members,respectively, to be compressed between cooperating ridges on said firstand second members as the respective ridges become radially aligned andto sequentially expand as said ridges move beyond radial alignment, saidelastic members engaging with succeeding adjacent pairs of ridges onsaid first and second members to establish a rotationally displacedposition of one of said first and second members with respect to theother thereof.
 2. The combination according to claim 1 wherein saidelastic members are cylinders extending axially in directions parallelto said ridges.
 3. The combination according to claim 2 wherein saidridges are formed by adjacent concave grooves formed in said internalsurface of said first member and in said external surface of said secondmember, said grooves having a radius substantially equal to that of saidelastic cylinders.
 4. The combination according to claim 3 wherein saidfirst member is connected to the stationary portion of said rotarydevice and said operator means for said rotary device is rotationallykeyed to said second member to cause rotational movement thereofrelative to said first member.
 5. The combination according to claim 1wherein: A represents the included angle between a pair of imaginarylines radiating from the axial center of said second member torespective ones of an adjacent pair of ridges on the external surface ofsaid second member; B represents the included angle between a pair ofimaginary lines radiating from the axial center of said first member torespective ones of an adjacent pair of ridges on the internal surface ofsaid first member; X represents the radial distance from the axialcenter of said first member to the ridges on the internal surfacethereof; Y represents the radial distance from the axial center of saidsecond member to the ridges on the external surface thereof; the sum ofangles A and B is the indexing angle for the detent and is divisibleinto three hundred sixty to result in a whole number quotient; and saidfirst and second members are constructed according to the relationship Ysin A/2 X B/2.
 6. The combination according to claim 5 wherein Drepresents the diameter of said circular elastic members and is found bythe formula D n Square Root X2 + Y2 + 2XY cos (A+B)/2 where n is afactor determined from the hardness of the material of said elasticcylinder and increases the diameter D inversely to increasing hardnessof the material.